Manufacture of alloy steel and iron



Patented Mar. l, 1927;

UNITED, STATES PATENT OFFICE.

BYRAMJI DQSAKLATWALLA, OF GRAFTON, PENNSYLVANIA.

MANUFACTURE OF ALLOY STEEL AND IRON.

No Drawing. Application filed July 16,

The present invention -relates to thenianufactureof alloy steel or iron, and more particularly to the reduction of the alloying elements directly from their ores, and the production of' the respective alloy steels and irons, without the introduction of excess carbon in the finished steel or iron. I

In the manufacture of alloy steels and irons, under the practice heretofore prevalent, the alloying elements, in the already reduced metallic state, mostly in the form of a ferro-alloy, are added to a molten bath of steel or iron. For example, to obtain the respective steels thereof, ferro-m'anganese, ferro-chromium, ferro-titanium, ferro-tung sten, ferro-vanadium, ferro-uranium, ferromolybdenum, ferro-nickel, or metallic nickel and ferro-cobalt or cobalt metal, are added to steel, in the molten state in the furnace, or after it is tapped in the ladle. As the regular commercial grades of such ferroalloys contain an appreciable amount of carbon, this practice introduces an undue amount of'carbon in the steel. If the special grades of low-carbon ferro-alloys are used, the cost of such alloys is. comparatively so high asto prohibitively increase the cost of steel produced. These defects are especially apparent in the case of steels Where the content of the alloying element has to be-high and the carbon content low, as in the case of the socalled stainless or rustless steels or irons, which have a chromium content of over 8% combined with a low carbon content.

It is not commercially practicable to use the regular high carbon ferro-alloys, and then decarbonize the steels after their addition, as theprocess of oxidizing the carbon is accompanied by an oxidation, and consequent waste, of the valuable alloying elements.

Another deficiency of the usual existing methods of manufacturing alloy steels, by the addition of metallic ferro-alloys to molten steel, is the phenomenon of segregation. The alloy being added in the'solid state in the form of lumps scattered over the surface of the molten steel, causes'points of concentration of the alloying elements at the location of each of the lumps. As the steel is tapped immediately after melting of the lumps in order to avoid an undue oxidation of the alloying elements, these points of higher concentration have no op- 1924. Serial No. 726,335.

the remainder of the alloy. Such a carbidecontaining ferro-alloy, when added to molten steel, will have the result that when the rest of the alloy will be completely assimilated, the carbide content will still be in the solid state, floating in the molten steel,without giving up its alloying element content to the bath. Such solid particles with a high alloying element content will persist in the steel on solidification and present segregation.

The above mentioned difficulties are overcome in the so-called direct reduction process by adding the alloying element to the bath of molten steel or iron in the form of oxide or ore and reducing it with a reducing agent incorporated in the steel. The reducing agent and the alloying material are added to a bath of steel consisting of a molten metal layer with a supernatant molten layer of slag, in such a manner that the alloying material is incorporated in the slag layer and the reducing agent is incorporated in the metal layer, and each thoroughly disseminated in their respective layers. With the alloying material, either mixed together or separately, are added fluxing materials which combine with the oxidation products of the reducing agent, thus eflecting its removal from the finished steel or iron and which also combine with the metalloids present in the molten steel, thus effecting a refining of the steel simultaneously with the alloying procedure. To effectively remove the last traces of the reduclngagent, and especially of carbon, the temperature at the end of the alloying and refining process is raised, which greatly a lzcelerates thechemical reactions taking p aoe.

If the total quantity of alloying material,

' such, for example, as chrome ore and fluxes is added at one time, owing to the refractory nature of the ore, it is a diflicult matter to melt it down into the slag layer and obtain a thorough dissemination. To overcome this difficulty only a certain amount of the ore and fluxes is charged at one time and the necessary reducing agent, which may be of the chrome oxide present in the slag layer.-

The reaction is then allowed to proceed between the slag layer and the metal layer, whereby the products of oxidation of the reducing agent, for instance, silica incase silicon was used as the reducing agent, transfer into the slag layer, helping to liquefy and flux the contents of the slag layer. As soon as the slag layer has assumed a visible fluidity owing to the. combination of the silica with the fluxes and gangue material of the ore, more alloying material is charged into the slag layer until the same has again assumed a viscous appearance. Then the correspondin amount of silicon is charged into the meta layer and the reactionallowed to take place until the slag layer has again alloying material will be assumed perfect fluidity. The 0 eration of charging alloying material an "reducin" agent successively is their continued until the necessary amount of alloying element has been incorporated in the molten! steel or iron. Thus, by charging the alloying material and reducing agent in successive portions, a visual means is obtained, by watching the fluidity of the slag layer, to follow-.

ing the alloying procedure and also to ourtail the time of the alloying rocedure as the liquefied by the help of chemical combination with the products of oxidation of the reducing agent and not by heat alone. By this procedure, therefore, heat energy will be saved.

Also by this procedure, after each successive step of alloying, the dead slag can be removed to a very great extent so that the useful furnace contents volume will not be occupied by waste slag. Thus a larger amount of steel can be melted and alloyed in this manner than if all the alloying material were charged in one portion. vThis fact is of special importance, where the steel or iron has to be alloyed to contain several percent of alloying metal, as in the case of the highchromium stainless or rustless steels or irons. 1

The slag to which the successive charges of ore are added is ve fluid, due to the silica introduced into it y the oxidation of the silicon reduclng agent. The strong fluxing action of the silica permits highly refractory ores to be charged into and assimilated by the slag. .The highly fluid slag is chemically active and the simultaneous refining of the steel by the removal of the objectionable metalloids, sulphur and phosphorus, is facilitated as well as the reduction of the alloying ore. Moreover, the fluidity of the slag causes a better circulation of the slag over the entire bath, thus giving less chance of segregations.

. i The reduced alloying metal is in contact with the molten steel or iron at the moment of its reduction, or in its .nascent state, consequentl the best conditions are obtained for t n e alloying and uniform dissemination of the, alloying metal throughout the steel. The alloying metal is obtained from a cheap source. The introduction of carbon andlse'gregation are avoided in the finished stee The process may be carried outin the following manner:

The, steel or iron, to which the alloying element is to be added, is melted down with the necessary fluxes, decarbonizing agents, etc. in an ordinary steel-making furnace, such as an open-hearth furnace, electric furnace, or other suitable furnace, so that a molten la er of metal with a supernatant layer of s ag is obtained. To this furnace bath is then added a portion of the raw alloying material, for instance, chrome ore, together with fluxes. Sufiicient temperature is maintained in the furnace to enable the added materials to melt into the slag layer, forming a viscous 1i uid. Without waiting to perfectly liquefy t is mass the calculated amount or a quantity'slightly less than the theoretical amount of reducin agent, such, for example, as silicon in the orm of ferrosilicon, is then charged into the furnace. The

'ferro-silicon' sinks through the slag layer and becomes incorporated in the metal layer. Reaction then sets in, between the metal layer and the slag; layer, whereby the slag layer gradually assumes increased fluidity as the silica formed enters into this'layer. When the slag layer assumes total fluidity, the

next successive portion of chrome ore and flux is charged followed by the equivalent charge of ferro-silicon'. This operation is repeated until a sample taken of the molten steel shows the desired chromium content. Then the temperature of the furnace is increased momentarily, if an electric furnace, by increasing the power input, to remove the last traces of SlllCOIl and carbon and the metal is tapped.

The successive charges of the reducing agent and alloying ore may be either charges,

consisting of the reducing agent and ore mixed together, or the reducing agent and ore may be added in charges which are separate as well as successive. It is preferred to add the reducing agent and the ore in separate as well as successive charges, as the reaction may be kept under a better regulated control thereby. By successive charging I mean adding the materials, in charges separated by sulficient time intervals to allow the reducing reaction to proceed to a substantial extent, and preferably toward completion,

before further char es areadded.

As fluxes with t e chrome ore may be used, lime, limestone, fluorspar, borax, sodamium alloy may be incorporated in the.

molten steel and its silicon content utilized to reduce a further quantity of'chromium from chrome ore added to the bath. This procedure is especially advantageous in the case of a steel containing a high percentage of the alloying element.

.ln the case of alloy steels containing a plurality of alloying elements, this procedure may be carried out in the same manner, the raw materials in the right proportions, containing the plural alloying elements, being charged together in each successive batch, or separately in the successive batches, on top of the'molten bath of steel. In such cases a flux may be separately added or the raw alloying materials may be selected of such composition as to have in their gangue the necessary fluxing cqmponents.

Also a plurality of reducing agents may be used, such as a mixture of carbonaceous and metallic reducing agents or metal carbides, or several different metallic reducing agents. For instance, a ferro-silicon alloy containing carbon may be used, both its silicon and carbon contents being utilized for the reduction purpose. Also any reducing agents originally present in the steel bath may be effectively used, in which case during the reduction operation, a simultaneous rcfining of the original steel will take place. Also the fluxes added with the alloying-element-containing raw material will have the secondary effect of refining the steel of the metalloid contents, such as sulphur and phosphorus, simultaneously with the reducing operation.

If desired, after reduction of the alloying element or elements in the steel, a small quantity of additional ferro-silicon or ferromanganese may be added as a. deoxidizing cleanser, before tapping, as in the common practicein making alloy steels. Also additions of other metals such as titanium, zirconium, copper, nickel, etc., may be used.

If desired these metals or scrap may be added between the successive chargings of the ore and reducing agent.

F The advantages of thls process of alloying are especially marked in the case of using silicon as a reducing agent, and producing steel or iron with a high alloycontent and .very low carbon content.

As such an instance may be cited the manufacture of socalled stainless or rustless iron containing over 8% chromium and less than 0.1% carbon. Also the advantages of this process; are apparent in the case of alloyinga highly oxidizable and diflicultly soluble element as uranium in steel. The alloying element being produced in the nascent state and directly in contact with the steel, the chances of its oxidizing or not dissolving are reduced to a minimum. Also, as the carbon content of the finished steel can be eliminated to any desired extent, simultaneously during the process of reducing, the exact percentage of carbon in the finished alloy steel can be arrived at more accurately by recarbonizing before tapping. In the case of metallic reducing agents being used their presence in the finished steel is practically eliminated by the action of fluxes and virtually completely removed by finally'increasin I the temperature. Thus by the process 0 this invention a steel of predetermined given composition can be more accurately pro duced than by the use of f'erro-all-oys. Also by this process, as the valuable alloying elements do not exist. at any time in the metallic state, unless dissolved and alloyed in the steel itself, and as after their solution in the steel there is no occasion to subject such steel to an oxidizing process for removal of carbon, for instance, as in the older processes, there is no loss suffered through oxidation, rendering the process extremely economical. Also as the molten steel always carries an amount of reducing agent during the entire process, it is protected from absorbing oxides in it, thus producing a much cleaner finished steel in the solid state.

While the preferred method of carrying out my process has been specifically described, it is to be understood that the invention is not limited to all of the described details, but may be otherwise embodied in 'layer, incorporating into the metal layer successive charges of a reducing agent the oxidation products of which render the slag more fluid and incorporating into the slag layer successive charges of an unreduc ed compound of the alloying metal, and malntaining the bath at a temperature suflicient to cause a reaction between the reducing agent in the metal layer and the unreduced compound of the alloying metal in the slag layer to thereby directly reduce the alloying metal in the bath, substantially as described.

2. The process of making chrome steel or iron, comprising forming a molten bath of steel or iron having a metal layer and a slag layer, charging into the bath successive charges of both a silicon reducing agent and chrome ore, the silicon reducing agent sinking through the slag layer and becoming incorporated in the metal layer and the chrome ore remaining in the slag layer and becoming incorporated therein, and maintaining the bath at a temperature suflicient to cause a reaction between the silicon in the metal layer and the chrome ore in the slag layer to thereby directly reduce chromium in the bath, substantially as described.

3. The process of making alloy steel or iron, comprising forming a bath of molten steel or iron having a metal layer and a slag layer, charging into said bath successive portions of both silicon and chrome ore and allowing sufficient time between successive charges to permit the silica produced by the oxidation of silicon to render the slag fluid, substantially as described.

4. The process of making alloy steel or iron, comprising forming a molten bath of steel or iron having ametal layer and a slag layer, adding to such bath in successive charges both an unreduced compound of the alloying metal and a reducing agent the oxidation products of which render the slag more fluid, and allowing sufiicient time between successive charges for the reducing reaction to proceed to such point that the oxidation products of .the reducing agent materially increase the fluidity of the slag, substantially as described.

5. The process of making alloy steel or iron, comprising forming a molten bath of steel or iron having a metal layer and a slag layer, and adding to such bath a reducing agent the oxidation products of which render the slag more fluid, an unreduced compound of the alloying metal and a fluxing material, each in successive charges alternating with charges of the other charged materials, substantially as described.

6. The process of making alloy steel or iron, comprising forming a molten bath of steel or iron having a metal layer and a slag layer, adding to such bath a reducing agent the oxidation products of which renderthe slag more fluid, an unreduced compound of the alloying metal and a fluxing material, each in successive charges alternating with charges of the other charged materials, and periodically tapping off the dead slag, substantially as described.

7. The process of making alloy steel or iron, comprising forming a molten bath of steel or iron having a metal layer and a slag layer, adding to such bath in successive charges an unreduced compound of the alloying metal, a metalloid absorbing fluxing material and a reducing agent the oxidation products of which render the slag more fluid, and allowing sufiicient time between charges for the reducing reaction to proceed to such point that the oxidation. products of the reducing agent materially increase the fluidity of the slag, combined with a simultaneous refining of the iron andsteel, substantially as described.

8. The process of making chrome steel or iron, comprising forming a' molten bath of steel or iron having a metal layer and a slag layer, adding to such bath in successive charges chrome ore, a metalloid absorbing fiuxing material and a silicon reducing agent, allowing sufficient time between successive charges for the reducing reaction to proceed to such pointthat the silica produced materially increases the fluidity of the slag, combined with a simultaneous refining of the iron or steel to take place, and periodically tapping elf the deadslag, substantially as described.

In testimony whereof I have hereunto set my hand.

BYRAMJ I D. SAKLATWALLA. 

